The present invention relates to an improvement of small-sized, high capacity nickel-metal hydride storage batteries composed of a nickel positive electrode, a hydrogen storage alloy negative electrode, a separator and an alkaline electrolyte.
A nickel-metal hydride storage battery is a secondary battery comprising a positive electrode formed from an active material composed mainly of nickel hydroxide and a negative electrode composed mainly of a hydrogen storage alloy, and has been widely used as a power source of portable equipment. However, an increase in the capacity has been desired for the further spread thereof. Noting the nickel-metal hydride storage batteries of a cylindrical type, at present, an electrode group inserted into a metal case generally has a so-called spiral structure in which a positive electrode plate, a negative electrode plate and a separator for separating these electrode plates from each other are wound in a spiral form. However, the electrode group with this spiral structure has such problems that a large amount of the separator which does not contribute to the battery capacity is present at the beginning of the winding and at the end of the winding, and a useless volume portion is present at the end of the winding because of its non-concentric form.
Regarding the method of constructing the electrode group, in order to solve the above problems, Japanese Laid-Open Utility Model Publication (Jitsukaisho) No. 58-24967 proposes an alkaline storage battery formed by combining a cylindrical sintered-type electrode and a columnar sinteredtype electrode. This makes it possible to easily insert the electrode group into a metal case. However, since the electrodes use a porous sintered nickel substrate with a porosity of about 80% obtained by sintering a nickel powder, the porosity of the substrate can not be increased any more, and thus the filling efficiency of an active material is low and an increase in the capacity is limited.
Then, in order to further increase the capacity there were invented the following nickel-metal hydride storage batteries (Japanese Laid-Open Patent Publication (Tokukaihei) No. 6-215796) employing a so-called pasted type electrode using a metal core made of a foamed metal porous body which has a large porosity and is capable of being filled with a large amount of an active material, or metal fiber, carbon fiber, metal mesh, punching metal, expanded metal, etc. Namely, a battery formed by layering a columnar electrode of one polarity and a hollow cylindrical electrode of the other polarity in the form of, concentric circles with a separator interposed therebetween so that the columnar electrode is located in the center, and a nickel-metal hydride storage battery formed by layering, round a columnar electrode of one polarity, a separator, a hollow cylindrical electrode of the other polarity, a separator and a hollow cylindrical electrode of the one polarity in this order. This makes it possible to achieve a drastic increase in the capacity.
However, there are the following problems in the structure of the electrode group in which, round a columnar electrode of one polarity, a hollow cylindrical electrode of the other polarity is layered in the form of concentric circles with a separator interposed therebetween and in the structure of the electrode group in which, round a cylindrical electrode of one polarity, a separator, a hollow cylindrical electrode of the other polarity, a separator and a hollow cylindrical electrode of the one polarity are layered in this order.
The first problem is a characteristic problem that an actual battery capacity at a specific high-current discharge is much lower than that of batteries with a conventional structure because the area of the mutually facing electrodes is small. The second problem is a productive problem that, in a state in which the electrode group is being inserted in the metal case, it takes a long time to inject an electrolyte.
The present invention ensures a certain area or more area of facing positive and negative electrodes by an electrode group structure in which electrodes of different polarities are repeatedly layered in the form of concentric circles with a separator interposed therebetween, and thereby solving the above-mentioned first problem.
The present invention forms an electrode serving as the center of an electrode group in a hollow cylindrical shape to facilitate the injection of an electrolyte into the hollow section, or layered electrodes in many layers to facilitate the injection of an electrolyte into a separator between the electrodes, and thereby solving the second problem.
The present invention provides a sealed cylindrical nickel-metal hydride storage battery comprising: an electrode group; a metal case for accommodating the electrode group; and a seal plate provided with a safety vent, for sealing an opening of the metal case, the electrode group being composed of at least one non-sintered type hollow cylindrical electrode of one polarity, at least one non-sintered type hollow cylindrical electrode of the other polarity and a separator for separating these electrodes from each other, wherein the electrodes are arranged alternately in the form of concentric circles with a separator interposed there between so that the electrode of the one polarity is located in the center.
Further, the present invention provides a sealed cylindrical nickel-metal hydride storage battery comprising: an electrode group; a metal case for accommodating the electrode group; and a seal plate provided with a safety vent, for sealing an opening of the metal case, the electrode group being composed of a non-sintered type columnar electrode of one polarity, at least one nonsintered type hollow cylindrical electrode of the one polarity, at least two non-sintered type hollow cylindrical electrodes of the other polarity and a separator for separating these electrodes from each other, wherein the cylindrical electrode of the other polarity and the cylindrical electrode of the one polarity are arranged alternately in the form of concentric circles with the separator interposed therebetween so that the columnar electrode of the one polarity is located in the center.